SOUND-SIGNALS. 



729 



FIG. 6. 



This diagram shows the result of observations at Little Gull Island, Long Island Sound, Aug. 9, 1881, beginning at 10 A. M. 

 Thermometer, dry bulb, 78-09 ; wet bulb, 73 F. Barometer, 2<J'77. Wind 8. W., force 8. Cir. Btrat. clouds about the 

 horizon. 



poses, taken from the tabulated schedule of our 

 notes. 



At 4 P. M. two of us went in a row-boat to 

 Little Gull, from the steamer which lay at 

 anchor half a mile off, and verified the fact 

 that the fog-signal had been in full operation 

 during the time of our observations. It then 

 occurred to us to investigate still more closely 

 what appeared to be a space, a circle of silence, 

 in which, during the experiments of the morn- 

 ing, we had failed to hear the signal. After 

 having had the siren put in full operation again, 

 we pulled toward the nearer end of Great Gull 

 island, the siren sounding meantime with ear- 

 splitting force. When about 600 yards away, 

 we suddenly lost the sound as completely as if 

 the signal had stopped. Pulling toward the 

 steamer, not more than 200 yards, we reached 

 a position at right angles with the axis of the 

 siren's trumpet, when we suddenly heard the 

 sound again at its full force. Thus, in pulling 



500 yards, we passed from complete audition 

 of the signal to absolute inaudition; and then 

 we passed back again to complete audition by 

 pulling 200 yards in another direction. All 

 this took place within half an hour, in open 

 water, always in full view of the signal-sta- 

 tion, and without any visible obstacle being 

 interposed or removed. While on the island 

 we learned that one of the light house keep- 

 ers, who had been on leave, had just returned 

 from Sag Harbor, twenty miles to the south- 

 east. He had failed to hear the signal at all. 

 until opposite the eastern end of Great Gull 

 island, and until he was within half a mile of 

 the siren, which was in full operation. 



The next morning our steamer anchored 

 about a mile north of Little Gull ; the wind 

 was light, the air was clear, and the day was 

 warm and beautiful. As it had been preceded 

 by a warm night, the atmosphere was homo- 

 geneous, and it was expected that we should 



